Mechanisms And Methods To Increase The Algae Removal Efficiency Of Modified Clays

In recent years coastal water eutrophication caused by human activities promoted its happening worldwide and caused profound and deleterious effects on aquatic ecosystems, aquaculture, tourism and public health. The control of HABs and the mitigation of their effects using clay is a promising method worldwide and it has been fully implemented in the field, with good results reported in Japan, South Korea and China. However, natural clay was inefficient in the removal of algae cells. The clay surface modification theory was proposed to increase the removal efficiency and the polyaluminum chloride modified clay prepared significantly improved the removal efficiency. However, PAC-MC was found to be easily affected by seawater. It is necessary to study the effects of the environmental factors of seawater to the removal efficiencies of modified clays to further improve the efficiency. We also studied the removal efficiencies of AC-MC and AS-MC and analyzed their removal mechanism. We also introduced ―bridging‖ effects, ―killing‖ effects and ―oxidation‖ effects into the flocculation process to explore the methods that could be used to further improve the removal efficiency. The main results were as follows.(1) The effects of the properties of the clay suspension on the removal efficiency of PAC-MCThe presence of sulfate ions in the PAC-MC suspensions was one of the factors that caused the DW and SW suspensions to have different abilities to remove harmful algal cells. Sulfate in the PAC-MC suspension showed a ―V‖-shaped effects and removing sulfate in modified suspension could improve the algae removal efficiency.(2) The removal efficiencies of AC-MC and AS-MCWe found the removal efficiency of AC-MC and AS-MC was influenced by dispersion medium, percentage of modifier in modified clay, suspension pH, algae pH and EOM in algae culture. AC-MC and AS-MC was little affected by the dispersion medium and showed strong abilities in removing algae cells.(3) Exploratory studies on the methods that could further improve the algae removalefficiencies of modified claysThe results showed that the removal efficiency of PAC-PAM modified clay or PAC-PDM modified clay was influenced by preparation methods, addition methods, and dispersion medium, among which the dispersion medium showed the most influences. Great difference may exist in removing freshwater and seawater HABs by organic macromolecule-inorganic modified clay.1 mg/L Hexadecyl trimethyl ammonium Bromide(HDTMA) or 2.5 mg/L Dodecyl dimethyl benzyl ammonium bromide(DDBAB) can kill the Phaeocystis globosa effectively regardless of dispersion medium. Good removal effects were obtained when HDTMA or DDBAB and inorganic modified clay was added sepraterly.The results showed that KHSO5 further improved the removal efficiency of inorganic modified clay and the inorganic-oxidation modified clay further improved the efficiency at which P. globosa was removed. Besides, the growth of P. globosa was significantly depressed by inorganic-oxidation modified clay compared with the addition of AS-MC. All the three components, clay, aluminum sulfate and KHSO5, showed significant influences on the removal efficiency(p<0.01) and aluminum sulfate and KHSO5 showed significant interactions on the removal efficiency(p<0.01).